1. Field of the Invention
The present invention relates generally to a mine roof support and, more particularly, to a system and method for creating a mine roof counter bore adapted to receive a crater plate and cable bolt head therein.
2. Description of Related Art
In mine work, such as coal mining, or in underground formations such as tunnels or other excavations, it is necessary to reinforce or support the roof and/or walls of the excavation to prevent rock falls or cave-ins. Among the most common means presently in use for effecting such support are cable bolts or other suitable elongated members, such as rod bolts, which are inserted into bore holes and exposed to a resin mixture or anchored therein to hold a metal support or bearing plate in tight engagement with the roof or wall surface. With respect to cable bolts, a resin system introduces resin capsules or cartridges into the bore hole and then advances the capsules to a blind end of the bore hole by the cable bolt backing the capsules. The spinning of the cable bolt ruptures the capsules and mixes the resin system supplied. Examples of prior art cable bolt arrangements are disclosed in U.S. Pat. Nos. 6,428,243; 5,586,839; and 5,064,311.
Each of the cable or rod bolts in the aforementioned prior art utilizes either a barrel and wedge assembly or a bolt head, respectively, to secure the metal support or bearing plate against the roof. Therefore, for example, the barrels of the cable bolts extend into the usable walk/crawl or transportation space in a mine, as defined by the distance from the floor to the ceiling of a mine tunnel. FIG. 1 depicts a prior art cable bolt including a multi-strand cable 3 secured to a barrel and wedge assembly 2 and situated with respect to a roofline of a mine. A washer 4 may be secured between a prior art bearing plate 6 and an existing barrel 8. A drive head, such as a nut 9, may be attached to a free end of the cable 3. An exemplary height of the prior art barrel and wedge assembly 2 is approximately three inches. Accordingly, several inches (not including the thickness of the prior art bearing plate 6) of material extends below the roofline. The prior art barrel and wedge assembly 2 used in connection with typical low-clearance tunnels requires that due care be exercised while moving within the tunnel, as the extending bolt heads may be engaged by moving equipment or mine personnel.